In order to compute the bearing capacity of the pile by either Meyerhof's or Nordlund's method, it

is first necessary to estimate the internal frictional angle for the soil. Based on gradation analysis

of the boring sample of the coral sands, 2 is assumed to be 35 degrees at the far end and

30 degrees at the head wall.

To determine the total bearing capacity Qu of the pile, use the formula

Qu = Qbu + Qsu = qbuAb + CsLfs

(1)

where

Qu

=

bearing capacity of the pile, kN or kips

Qbu

=

shaft friction, kN or kips

Qsu

=

toe bearing, kN or kips

qbu

=

toe bearing resistance, kPa or ksf

Ab

=

toe bearing area, m2 or ft2 = .258 m2 or 2.78 ft2

Cs

=

shaft circumference, m or ft = 2.032m or 6.67 ft

L

=

embedded length, m or ft = 16.159m or 53 ft

fs

=

maximum mobilized shaft friction, kPa or ksf

Toe Resistance -- Meyerhof Method

The Meyerhof method computes the toe bearing resistance by the formula

qbu = F'Nqp.p # q1 = NqptanN

(2)

q

where

F'1

=

effective overburden pressure at the pile toe,

kPa or ksf

=

geometry correction factor = 1

.p

q

Nqp

=

bearing capacity surcharge factor = 60 for

N = 30 degrees and 150 for N = 35 degrees

The effective overburden pressure is limited to the overburden pressure at the critical depth,

which is 10 times the pile size or in this case Lc = 5.08 m (16.7'). This can be computed by the

equation

N'l = Lc((sat-(w) = 42 kPa (.877 ksf)

(3)

where

=

18.1 kPa/m (.115 ksf/ft)

(sat

=

9.82 kPa/m (.0625 ksf/ft)

(w

Solving equation (2) using the N'l from equation (3), qbu = 6,272 kPa (131 ksf) at the headwall

and 2,921 kPa (61 ksf) at the far end. Both of these values exceed the q1 from equation (2);

therefore, for the first term of equation (1), the toe capacity by the Meyerhof method is

Qbu = 1,299 kN (292 kips)

(4a Headwall, N = 11)

Qbu = 427 kN (96 kips)

(4b Far End, N = 6)

d)

(sheet 1 of 3)

Figure 5-7. Pile capacity by Meyerhof and Nordlund methods.

5-12

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